Kort nozzle



March 1o, 1970 J, ,ANTHES En.. 3,499,412

` KORTNOZZLIE Filed Feb. 8, 1968 MS2/@fha @w ATTORNEYS.

United States Patent O U.S. Cl. 11S-42 7 Claims ABSTRACT OF THEDISCLOSURE This application discloses the combination of a screwpropeller surrounded by a Kort type nozzle where an added flow of wateris induced along the inside wall of the nozzle to relieve cavitation atthe tips of the propeller blade. This is effected by discharging wateraround the forward end of the nozzle through a slit so arranged thatwater forced through the slit flows under influence of the so-calledCoanda effect along the inner wall of the nozzle. The ow may be adjustedby controlling the water supply to the slit and additional thrust may beobtained from the added flow of water.

BACKGROUND OF THE INVENTION Field of the invention The present inventionrelates to improvements in propulsion devices of the propeller type inwhich the propeller works in a surrounding nozzle.

Description of the prior art It is known in the art of ship propulsionto surround the propeller with an annular nozzle structure which is ofsubstantially airfoil section with the passage therethrough of aventuri-like contour with the propeller being positioned in the passageat the place of greatest restriction and with the propeller blade tipshaving a working clearance with the inner wall of the nozzle structure.Such a nozzle arrangement is shown in U.S. Patent 2,030,-

375', issued Feb. 11, 1936 and is now generally known in the art as aKort-type nozzle. Such an arrangement is most widely used on rivertow-boats where the maximum diameter of the propeller is restricted bythe relatively shallow channels and thrust cannotbe increased byincreasing the diameter of the propeller, so that any increase in thrustis important, and is also of importance for increasing rudder responsefor manuvering the boat and its tow along a winding course.

One of the things which now limits the maximum thrust for any givendiameter of propeller is cavitation in the region of the propeller tips.Due to drag or friction of the water along the walls of the nozzle,'thevelocity of the water entering the nozzle is diminished in the regionimmediately adjacent to the interior wall of the nozzle s O that it isdifferent from the ow of the water elsewhere through the passage,resulting in cavitation at the propeller blade tips. In order toavoid'or reduce this effect, it is the usual practice to design thepropeller blades in such manner that the propeller blades have a reducedpitch at their tip regions rather than a constant pitch throughout. Thisreduces the maximum power absorption, and complicates the propellerdesign.

SUMMARY Briefly, the present invention provides a nozzle in combinationwith a screw-like propeller for increasing the propulsive efficiency ofthe propeller and for producing a thrust in addition to that produced bythe propeller.

According to this invention, the nozzle isprovided at its forward endwith a substantially annular radially di- ICC rected opening or slitthrough which a controlled flow of water is discharged from an annularduct inside the nozzle. A pipe opening into this duct, which may also bethe supporting post for the nozzle, is connected with a pump. The slitis so formed between front and rear lip portions arranged to increasethe flow of water through the nozzle adjacent to its interior wall by aphenomenon known as the Coanda effect and thereby relieve the cavitationat the propeller blade tips. This Coanda effect which in a crude way isevidenced by the flow of water down the outside of a glass of water whenthe glass is tipped for pouring, is discussed in the .lune 1966 issue ofScientific American, pps. 84-92.

Accordingly, with the improved Kort nozzle of this invention, it ispossible to counteract the drag effect of the walls of the nozzle on thewater owing through the nozzle and thus reduce or eliminate cavitationand enable the use of a propeller with a uniform pitch throughout, thussimplifying its design and provide a propeller having greater thrust fora given diameter over propellers heretofore used in conjunction withnozzles.

It is therefore a primary object of the present invention to provide animproved Kort nozzle and propellerl arrangement wherein cavitation inthe tip region of the propeller blades is substantially eliminated, thusallowing use of a propeller of constant pitch throughout, and to providea Kort nozzle of unique construction.

These and other objects of the present invention will become moreapparent by referring to the following detailed specification andclaims.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a side elevation of apartially shown stern of a vessel and the propeller, with the improvedKort nozzle of the present invention being shown in longitudinalsection.

FIG. 2 is a longitudinal section through the improved Kort nozzle shownin FIG. l on a larger scale with the propeller being shown in dottedline.

FIG. 3 is a fragmentary longitudinal sectional view on a larger scale tomore clearly show the lip arrangement defining the slit.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, 10designates schematically the stern of a ship with a propeller shaft 11and a propeller 12. The propeller is positioned in the passage 13 in aKort-type nozzle of the usual contour, in which the nozzle comprises anannulus 14 of generally airfoil contour, thickest at its forward orentering end 15 and tapering to the rear or trailing end 15. The passage13 is of a venturilike shape with the propeller in the region ofgreatest restriction. Asv shown in the drawing and as customary in theart for the reason hereinbefore explained, the propeller has a diametersuch that there is only a good working clearance between the tips of thepropeller blades and the inside wall of the nozzle.

There is an annular duct 16 in the annulus, and a water supply pipe 17,which may also be a supporting post for the nozzle which opens into duct16. The pipe 17 is connected to a source of water, indicated by pump 18on the ship and a conduit 19 leading from the pump to the pipe 17. Arestricted substantially annular passage leads forwardly from the duct16 to a substantially annular discharge opening 20. This opening is aslit formed between confronting annular lip portions 21 and 22constituting part of the forward end of the nozzle. The opening isdirected substantially radially inward and communicates with thepassageway 13, and the rear lip 21 is formed with a step or relief 23immediately adjacent the slit and arranged to increase the Coanda effectby which the water,

flowing radially from the slit, travels rearwardly in a layer likestream adjacent to the inner wall or surface of nozzle. Its rate of flowcan be controlled and adjusted by controlling the output from the pump18 or otherwise throttling it. By this arrangement the drag against theinterior surface of the nozzle is relived, and a stream flow is inducedaround the inner wall of the nozzle by means other than the propelleritself. As a result, there is adequate velocity to relieve cavitation atthe propeller blade tips. While energy of course is required to operatethe pump, it is utilized by decreasing the drag of water through thenozzle and water issuing from the slit and moving rearwardly along thenozzle produces some forward thrust which is added to the thrust of thepropeller thereby adding to the thrust without increasing the propellersize.

While the invention has particular application to ship propulsion it maybe used elsewhere where a venturi-like nozzle is employed in combinationwith a propeller type means which induces a main flow of fluid throughthe nozzle and it is desirable to induce an additional ow of fluidadjacent to the interior surface of the nozzle to reduce drag resultingfrom contact of the main flow of lluid with the interior surface of thenozzle.

It is to be further understood that the above described embodiment ofthe invention is simply illustrative and numerous other arrangements maybe readily devised by those skilled in the art which will embody theprinciples of the invention and fall within the spirit and scope thereofand within the scope of the following claims.

We claim:

1. The combination comprising:

(a) a nozzle comprising an annulus of substantially air foil sectionwith the forward end of the annulus being thicker than the trailing endsuch that a venturilike passageway is defined therethrough,

(b) a screw propeller about which the nozzle is positioned for inducinga main ow of water through the passageway,

(c) means located at the forward end of the annulus for inducing a flowof water through the passageway adjacent to the interior surface of theannulus in addition to the main flow of water induced by the propellerthrough the passageway, and

(d) means independent of an external to the nozzle for supplying waterunder pressure to said last-named means.

2. A Kort-type nozzle having entering and trailing ends with asubstantially annular radially-directed opening in the entering endthereof with a substantially annular Coanda surface therearound adjacentthe outlet of said opening, a screw propeller having pitched bladesabout which the nozzle is positioned for inducing a main flow of waterthrough the nozzle and means comprising a source of water under pressurefor discharging water through the radially-directed opening in a streamalong the interior surface of the nozzle in addition to the main flow ofwater induced by the propeller through the nozzle to reduce dragresulting from contact of the main flow of water with the interiorsurface of the nozzle and thereby relieve cavitation producingconditions at the tips of the screw propeller blades.

3. The combination comprising:

(a) a nozzle comprising an annulus of substantially air' foil sectionwith the forward end of the annulus being thicker than the trailing endsuch that a venturi-like passageway is defined therethrough, the forwardend of the annulus having a substantially annular radially-directedopening therein communicating with the passageway, the annulus having aninternal duct opening into said annular radially-directed opening,

(b) a screw propeller having pitched blades about which the nozzle ispositioned for inducing a main ow of water through the passageway, and

(c) means comprising a source of water under pressure independent of thenozzle for supplying water to said internal duct for discharge throughthe radially-directed opening along the interior surface of thepassageway between the main flow of water induced by the propellerthrough the passageway and the interior wall of the passageway.

4. The combination as set forth in claim 3 wherein the opening in theforward end of the annulus is provided between spaced forward andtrailing annular lip portions defining between them a radially-directedslit-like opening, the trailing lip having an annular step immediatelyadjacent the slit-like opening in a position to increase the Coandaelfect of the water emerging from the slit-like opening.

5. The combination as set forth in claim 4 wherein said means forsupplying water to the internal duct includes a pipe constituting also asupporting post for the nozzle.

6. The combination as set forth in claim 4 wherein the means forsupplying the water to the internal duct is adjustable for varying thepressure of the tluid supplied thereto whereby the velocity of the wateremerging from the radially-directed opening may be adjusted.

7. In the combination of a nozzle member having a venturi-shapedpassageway therethrough with a powerdriven screw propeller positionedtransversely in the area of greatest restriction of the passageway witha working clearance between the periphery of the propeller and theinterior of the nozzle, the invention comprising:

(a) means in the nozzle arranged to induce a substantially annular llowof fluid through the nozzle along and in contact with the interior wallof the nozzle and independently of the llow induced through the nozzleby the rotation of the propeller in the nozzle, and- (b) means forsupplying uid under pressure from a source externally of the nozzle tosaid first-named means.

References Cited UNITED STATES PATENTS 1,730,748 10/ 1929 Schmidt230--122 2,864,236 12/1958 Toure et al 230-114 3,179,081 4/ 1965Backhaus et al 114--166 FOREIGN PATENTS 893,489 4/ 1962 Great Britain.935,340 2/ 1948 France.

ANDREW H. FARRELL, Primary Examiner U.S. Cl. X.R.

